Process for upgrading a hydrocarbonaceous feedstock

Abstract: Process for upgrading a hydrocarbonaceous feedstock substantially boiling in the gasoline range, which process comprises: a) subjecting the feedstock to a separation treatment and recovering therefrom a first hydrocarbon feed stream comprising C₆ and smaller hydrocarbons and a second hydrocarbon feed stream comprising C₆ and greater hydrocarbons; b) subjecting at least part of the second hydrocarbon feed stream to a separation treatment wherein normal paraffins and optionally mono-isoparaffins are separated from di-isoparaffins; c) recovering therefrom a first separation effluent stream comprising normal paraffins and optionally mono-isoparaffins and a second separation effluent stream comprising di-isoparaffins; d) subjecting at least part of the first separation effluent stream to a reforming step to produce a reformate; and e) subjecting at least part of the reformate obtained to a hydrogenation step.

Description: The present invention relates to a process for upgrading a hydrocarbonaceous feedstock substantially boiling in the gasoline range, to produce a gasoline blending pool having an enhanced octane content and a reduced aromatics content. One of the main objects in nowaday's oil refining is to produce gasolines fulfilling the increasing environmental demands on product quality and having a high octane number. EP-A-0 553 931 describes one such process already proposed for obtaining an octane-enhanced gasoline. This means for gasoline that the octane specification has now to be established without lead-containing additives, less aromatics, in particular benzene, less olefins and lower gasoline vapour pressure. Object of the present invention is to provide a process for the preparation of gasolines fulfilling both the increasing environmental demands on product quality and the high octane requirement. It has now been found that gasolines can be produced having a high octane number and a considerably reduced aromatics content, in particular benzene, when use is made of an upgrading process comprising a specific sequence of process steps. Accordingly, the present invention relates to a process for producing a gasoline blending pool having an enhanced octane content and a reduced aromatics content, which process comprises: a) subjecting a hydrocarbonaceous feedstock substantially boiling in the gasoline range to a separation treatment and recovering therefrom a first hydrocarbon feed stream comprising C 6 and smaller hydrocarbons and a second hydrocarbon feed stream comprising C 6 and greater hydrocarbons; b) subjecting at least part of the second hydrocarbon feed stream to a separation treatment wherein normal paraffins and optionally mono-isoparaffins are separated from di-isoparaffins; c) recovering therefrom a first separation effluent stream comprising normal paraffins and optionally mono-isoparaffins and a second separation effluent stream comprising di-isoparaffins; d) subjecting at least part of the first separation effluent stream to a reforming step to produce a reformate; e) subjecting at least part of the reformate obtained to a hydrogenation step; and f) passing the second separation effluent stream from step c) to a gasoline blending pool. In this way a direct octane enhancement of the resultant gasoline blending pool is established whilst a substantial reduction of aromatics content, in particular benzene, is realized. In refineries with restriction on production of gasoline due to octane and/or capacity limitations, this octane enhancement can permit increased gasoline production. The two hydrocarbon feed streams which are derived from the feedstock in step a) can suitably be obtained by distillation. Suitably, the two hydrocarbon feed streams are adjacent fractions obtained by distillation. Depending, of course, on the sharpness of the cutting points of the fractions chosen in the distillation some overlap may occur among the adjacent fractions. Preferably, the separation treatment in step a) is carried out in such a way that the first hydrocarbon feed stream substantially comprises C 5 and smaller hydrocarbons. If the first hydrocarbon feed stream substantially comprises C 5 and smaller hydrocarbons said feed stream does not need to be subjected to an isomerisation process but can advantageously directly be introduced in the gasoline blending pool. Suitably, at least part of the feedstock to be upgraded can be subjected to the hydrogenation in step e) before being subjected to the separation treatment in step a). The hydrocarbonaceous feedstock boiling in the gasoline range can suitably be obtained by distillation of crude or by catalytic cracking although it may be obtained by other cracking processes such as thermal cracking, delayed coking, visbreaking and flexicoking. Such gasoline feedstocks usually contain unacceptable levels of sulphur and nitrogen and benefit from a hydrotreatment before they are subjected to the process according to the present invention. Suitably, the process according to the present invention is carried out in such a way that in step b) both the normal paraffins and mono-isoparaffins (mono-branched paraffins) are separated from the di-isoparaffins (di-branched paraffins). This is suitably established by passing at least part of the second hydrocarbon feed stream to a separation zone comprising a shape-selective separatory molecular sieve having a pore size intermediate 5.5 x 5.5 to 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å, the pore size being sufficient to permit entry of normal paraffins and mono-isoparaffins but restrictive to prohibit entry of di-isoparaffins, other multi-branched paraffins, cyclic paraffins and aromatic hydrocarbons. In this way the normal paraffins and mono-isoparaffins can selectively be separated from the di-isoparaffins. Subsequently, the first separation effluent stream comprising both normal paraffins and mono-isoparaffins and the second separation effluent stream comprising di-isoparaffins can be recovered. Subsequently, at least part of said first separation effluent is subjected to the reforming step. Preferably, substantially the entire first separation effluent stream is subjected to the reforming stream, although also part thereof may be used as a preferred chemical feedstock. For instance, as a feedstock for a highly selective (dehydro)cyclization process. Preferably, the normal paraffins are firstly separated from the mono-isoparaffins and di-isoparaffins, whereas the mono-isoparaffins are subsequently separated from the di-isoparaffins. To this end use can be made of a multiple select adsorbent molecular sieve system having particular separatory qualities. Preferably, the multiple separatory sieve system to be used comprises a first molecular sieve having a pore size of 4.5 x 4.5 Å or smaller and being shaped to permit adsorption of normal paraffins in a selective manner vis-a-vis mono-isoparaffins, di-isoparaffins, other multi-branched paraffins, cyclic paraffins and aromatic hydrocarbons and a second molecular sieve having a pore size intermediate 5.5 x 5.5 to 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å, being selected to permit adsorption of mono-isoparaffins (and any remaining normal paraffins) in deference to di-isoparaffins, other multi-branched paraffins, cyclic paraffins and aromatic hydrocarbons which can be passed directly to a refinery gasoline blending pool. In operation, at least part of the second hydrocarbon feed stream is firstly contacted with the first shape-selective separatory molecular sieve as defined hereinabove to produce a first separation effluent stream comprising the normal paraffins and a second separation effluent stream comprising both mono- and di-isoparaffins. The latter separation effluent stream is subsequently contacted with the second shape-selective separatory molecular sieve as described hereinabove. Subsequently, a third separation effluent stream comprising mono-isoparaffins can be recovered and a fourth separation effluent stream comprising di-isoparaffins can be recovered. At least part of the first and third separation effluents can be subjected to the reforming step. Preferably, substantially the entire first and third separation effluent streams are subjected to the reforming step. In another embodiment of the present invention at least part of the first and third separation effluent streams may suitably be used as a preferred chemical feedstock as mentioned hereinbefore. The multiple select adsorbent molecular sieve system as described hereinabove comprises at least two molecular sieves. These can be arranged in separate vessels, or they can be arranged in a stacked flow scheme within one vessel. This first molecular sieve can be a calcium 5 Å zeolite or any other sieve of similar pore dimensions. It is not necessary to size the first sieve to adsorb all of the normal paraffins, but it is preferred so that the second molecular sieve does not have to function as a normal paraffin adsorption sieve. The second molecular sieve in this process sequence is exemplified by a molecular sieve which has eight and ten member rings and pore dimensions intermediate 5.5 x 5.5 and 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å. The preferred second molecular sieve of this invention is exemplified by a ferrierite molecular sieve. It is preferred that the ferrierite sieve be present in a hydrogen form, but it alternatively can be exchanged with a cation of an alkali metal, or alkaline earth metal or transition metal cation. The second molecular sieves of this invention include ferrierite and other analogous shape-selective materials with pore openings intermediate in dimensions to those of the calcium 5 Å zeolite and ZSM-5. Other examples of crystalline sieves include aluminophosphates, silicoaluminophosphates, and borosilicates. The aluminophosphate, silicoaluminophosphate and borosilicate molecular sieves which can be used as a second molecular sieve will have a pore opening intermediate 5.5 x 5.5 and 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å. It is feasible that the second molecular sieve comprises a large pore zeolite that has been ion exchanged with cations to diminish the effective pore size of the sieve to within the aforementioned range of dimensions. When applying multiple select adsorbent molecular sieve systems, the sequence of the sieves, whether in discrete vessels or in a stacked variety, is very important. If the sieves are interchanged the process loses effectiveness because the larger sieve will rapidly fill with normal paraffins, prohibiting the efficient adsorption of mono-isoparaffins. The respective sieves applied in a multiple select adsorbent molecular sieve system should be arranged in a process sequence to first provide adequate adsorption of the normal paraffin hydrocarbons, and then, adsorption of the mono-isoparaffins. Each of these respective sieves can be provided with a common desorbent stream or each sieve may have its own desorbent stream. The desorbent is preferably a gaseous material such as a hydrogen gas stream. Suitably, at least part of the reformate obtained in step d) is subjected to a separation treatment from which a light fraction comprising C 6 and smaller hydrocarbons and a heavy fraction comprising C 6 and greater hydrocarbons are recovered. Subsequently, at least part of the light fraction and optionally at least part of the heavy fraction are subjected to the hydrogenation in step e). Suitably, C 5 and smaller hydrocarbons are separated from the light fraction before the latter is subjected to the hydrogenation in step e). In the hydrogenation step any conventional hydrogenation catalyst can be applied. Exemplary of such a catalyst is a catalyst comprising at least one component of a Group VIII and/or Group VIb metal on a silica-alumina-containing carrier. Preferably, use is of a platinum component on an amorphous silica-alumina carrier. The hydrogenation step can suitably be carried out under conventional hydrogenation conditions. Typically the hydrogenation is carried out at a temperature between 150 to 300 °C and a partial hydrogen pressure of between 10 to 30 bar. Suitably, at least part of the light and heavy fraction is recovered. In another attractive embodiment of the process according to the present invention at least part of the light and heavy fraction is subjected to a separation treatment wherein normal paraffins and optionally mono-isoparaffins are separated from di-isoparaffins, and whereby a first hydrocarbon product stream comprising normal paraffins and optionally mono-isoparaffins and a second hydrocarbon product stream comprising di-isoparaffins is recovered. At least part of the first hydrocarbon product stream may be used as preferred chemical feedstock as mentioned hereinbefore. Suitably, the separation treatment is carried out in such a way that both the normal paraffins and mono-isoparaffins are separated from the di-isoparaffins. This is suitably established by passing at least part of the light and heavy fraction to a separation zone comprising a shape-selective separatory molecular sieve having a pore size intermediate 5.5 x 5.5 to 4.5 x 4.5 Å but excluding 4.5 x 4.5 Å, the pore size being sufficient to permit entry of normal paraffins and mono-isoparaffins but restrictive to prohibit entry of di-isoparaffins. In this way the normal paraffins and mono-isoparaffins can selectively be separated from the di-isoparaffins, other multi-branched paraffins, cyclic paraffins and aromatic hydrocarbons. Subsequently, a first hydrocarbon product stream comprising both normal paraffins and mono-isoparaffins and a second hydrocarbon product stream comprising di-isoparaffins can be recovered. Suitably, the separation treatment is carried out in such a way that the normal paraffins are firstly separated from the mono-isoparaffins and di-isoparaffins, whereas the mono-isoparaffins are subsequently separated from the di-isoparaffins. To this end use can be made of a multiple select adsorbent molecular sieve system as described hereinbefore. When use is made of such a multiple select adsorbent molecular sieve system upstream the reforming step, at least part of the light and heavy fraction is passed to the first molecular sieve. When use is made of a multiple select adsorbent molecular sieve system both upstream and downstream of the reforming step, firstly initially present normal and mono-isoparaffins are separated from di-isoparaffins, whereas subsequently normal paraffins and mono-isoparaffins which have been produced in the reforming step, are separated from di-isoparaffins. The application of a multiple select adsorbent molecular sieve system both upstream and downstream of the reforming step is very attractive since it offers product flexibility together with product quality. Hence, in a preferred embodiment of the present invention a multiple select adsorbent molecular sieve system is applied both upstream and downstream the reforming step. The separation treatments upstream and downstream of the reforming step wherein the normal paraffins and optionally the mono-isoparaffins are separated from di-isoparaffins are preferably carried out in the same separation zone. Suitably, the light fraction comprising C 6 and smaller hydrocarbons and the heavy fraction comprising C 6 and greater hydrocarbons have been obtained from the reformate by means of distillation. Suitably, the light and the heavy fraction are adjacent fractions obtained by distillation. Depending, of course, on the sharpness of the cutting points of the fractions chosen in the distillation some overlap may occur among the adjacent fractions. In another embodiment of the present invention the reformate obtained in step d) is firstly subjected to a separation treatment wherein a gaseous fraction is separated from a liquid fraction, whereafter the liquid fraction is separated into the light fraction comprising C 6 and smaller hydrocarbons and the heavy fraction comprising C 6 and greater hydrocarbons. In the reforming step any conventional reforming catalyst can be applied. Preferably, in the reforming step a catalyst is applied having a substantial (dehydro)cyclization selectivity. Exemplary of such a catalyst is a platinum-containing catalyst with platinum present in for instance a range of 0.005 wt% to 10.0 wt%. The catalytic metals associated with the reforming function are preferably noble metals from Group VIII of the Periodic Table of elements, such as platinum and palladium. The reforming catalyst can be present per se or it may be mixed with a binder material. It is well appreciated that the application of noble metal(s)-containing reforming catalysts normally requires a pretreatment in the form of a catalytic hydrotreatment of the feedstock to be upgraded. In this way nitrogen-compounds and sulphur-compounds can be removed from the feedstock which compounds would otherwise reduce the performance of the reforming catalyst considerably. The reforming step can suitably be carried out under conventional reforming conditions. Typically the process is carried out at a temperature from 450 to 550 0 C and a pressure of 3 to 20 bar. The reaction section in which the reforming step is to be performed can suitably be separated into several stages or reactors. The present invention will now be illustrated by means of the Example. Example A process according to the present invention is carried out in accordance with the flow diagram as schematically shown in Figure 1. A hydrocarbonaceous feedstock substantially boiling in the gasoline range and having the properties as set out in Table 1 is introduced via a line 1 and a line 1a into a distillation column 2 in which the feedstock is separated into two hydrocarbon feed streams. A first hydrocarbon feed stream comprising C 5 and smaller hydrocarbons is withdrawn via a line 3 and introduced into a gasoline blending pool 4. A second hydrocarbon feed stream comprising C 5 and greater hydrocarbons is withdrawn via a line 5, and passed to a separation zone 6 which contains two molecular sieves 7 and 8. Molecular sieve #1 (7) is a commercial zeolite having a pore size from 4.5 to 4.5 Å or smaller. Molecular sieve 8, referred to as molecular sieve #2, has a pore size of 5.5 x 5.5 to 4.5 x 4.5 Å, but excludes 4.5 x 4.5 Å. The first molecular sieve 7 selectively adsorbs normal paraffins in preference to mono-isoparaffins, di-isoparaffins, other multi-branched paraffins, cyclic paraffins and aromatic hydrocarbons. A fraction comprising normal paraffins is withdrawn via a line 9 and introduced into a reforming reactor 10. The separation effluent stream substantially freed from normal paraffins is withdrawn via a line 11 and contacted with molecular sieve #2(8). In this molecular sieve, mono-isoparaffins are adsorbed while di-isoparaffins and other multi-branched paraffins, and cyclic paraffins are passed through the sieve without adsorption. A fraction comprising mono-isoparaffins is withdrawn via a line 12 and introduced in the reforming reactor 10. The remaining separation effluent (di-isoparaffins fraction) which is now substantially freed from normal paraffins and mono-isoparaffins is withdrawn via a line 13 and introduced in the gasoline blending pool 4. In the reforming step use is made of a commercially available highly selective (dehydro)cyclization catalyst under typical semi-regenerative reforming conditions. The reformate obtained is subsequently withdrawn via a line 14 and introduced into a distillation column 15. In the distillation column 15 the reformate is separated into a gaseous fraction and a liquid fraction. The gaseous fraction is withdrawn via a line 16, the liquid fraction is withdrawn via a line 17. The liquid fraction is subsequently passed to a distillation column 18. In the distillation column 18 the liquid fraction is separated into a first fraction comprising C 5 and smaller hydrocarbons, a second fraction comprising C 6 and C 7 hydrocarbons and a third fraction comprising C 7 and greater hydrocarbons. The first fraction is withdrawn from the distillation column 18 via a line 19 and introduced into the gasoline blending pool 4. The second fraction is passed to a hydrogenation unit 20 via line 21. A hydrogen stream is introduced into the hydrogenation unit 20 via a line 22. The hydrogenated product obtained from the hydrogenation unit 20 is then co-processed with the feedstock to be upgraded via lines 23 and 1a. The third fraction is withdrawn from the distillation column 18 via a line 24 and introduced into the gasoline blending pool 4. 100 pbw of the feedstock in line 1 yields the various product fractions in the following quantities: 11.7 pbw first hydrocarbon feed stream (line 3) 107.3 pbw second hydrocarbon feed stream (line 5) 21.6 pbw normal paraffins fraction (line 9) 85.7 pbw a first part separation effluent stream (line 11) 23.3 pbm a mono-isoparaffins fraction (line 12) 62.4 pbw di-isoparaffins fraction (line 13) 44.9 pbw reformate fraction (line 14) 5.8 pbw gaseous fraction (line 16) 39.1 pbw liquid fraction (line 17) 1.4 pbw first fraction (line 19) 18.1 pbw second fraction (line 21) 0.9 pbw hydrogen stream (line 22) 19.0 pbw hydrogenated product stream (line 23) 19.6 pbw third fraction (line 24) In the blending gasoline pool 4, 5.3 pbw of butane 17.5 pbw of MTBE are added to the gasoline obtained via a line 25. In this way 117.9 pbw of an overall gasoline is obtained having the maximum allowable RVP specification. The overall gasoline obtained in the blending pool 4 has the properties as set out in Table 2. From Table 2 it is clear that a very attractive gasoline, in terms of octane number and content of aromatics, in particular benzene, can be obtained by applying the present invention. In conventional upgrading processes gasolines are obtained having a considerable higher content of aromatics, in particular benzene. C (%wt) 85.2 H (%wt) 14.8 S (ppmw) < 1 d (15/4) 0.731 I.B.P. 56 10% wt rec. 64 30% " " 92 50% " " 106 70% " " 127 90% " " 149 F.B.P. 197 RON 55.7 naphthenes " 27.2 aromatics " 10.3 Gasoline properties: RON 95.0 total aromatics (%vol) 23.2 benzene (%vol) 1.1 naphthenes (%vol) 37.5 RVP (kPa) 60

Claims: Process for producing a gasoline blending pool having an enhanced octane content and a reduced aromatics content, which process comprises: a) subjecting a hydrocarbonaceous feedstock substantially boiling in the gasoline range to a separation treatment and recovering therefrom a first hydrocarbon feed stream comprising C 6 and smaller hydrocarbons and a second hydrocarbon feed stream comprising C 6 and greater hydrocarbons; b) subjecting at least part of the second hydrocarbon feed stream to a separation treatment wherein normal paraffins and optionally mono-isoparaffins are separated from di-isoparaffins; c) recovering therefrom a first separation effluent stream comprising normal paraffins and optionally mono-isoparaffins and a second separation effluent stream comprising di-isoparaffins; d) subjecting at least part of the first separation effluent stream to a reforming step to produce a reformate; e) subjecting at least part of the reformate obtained to a hydrogenation step; and f) passing the second separation effluent stream from step c) to a gasoline blending pool. Process according to claim 1, wherein in step b) both the normal paraffins and mono-isoparaffins are separated from the di-isoparaffins, and at least part of the normal paraffins and mono-isoparaffins so obtained is subjected to the reforming step. Process according to claim 2, wherein firstly the normal paraffins are separated from the isoparaffins, and subsequently the mono-isoparaffins are separated from the di-isoparaffins. Process according to any one of claims 1-3, wherein at least part of the reformate stream obtained in step d) is separated into a light fraction comprising C 6 and smaller hydrocarbons and a heavy fraction comprising C 6 and greater hydrocarbons, whereby at least part of the light fraction and at least part of the heavy fraction is subjected to the hydrogenation in step e). Process according to claim 4, wherein at least part of the reformate is firstly separated into a gaseous fraction and a liquid fraction, whereafter the liquid fraction is separated into the light fraction comprising C 6 and smaller hydrocarbons and the heavy fraction comprising C 6 and greater hydrocarbons. Process according to claim 4 or 5 wherein at least part of the light fraction and at least part of the heavy fraction is subjected to a separation treatment wherein normal paraffins and optionally mono-isoparaffins are separated from di-isoparaffins, and whereby a first hydrocarbon product stream comprising normal paraffins and optionally mono-isoparaffins and a second hydrocarbon product stream comprising di-isoparaffins is recovered, which second hydrocarbon product stream is passed to the gasoline blending pool Process according to claim 6, wherein the separation treatment is carried out in such a way that both the normal paraffins and mono-isoparaffins are separated from the di-isoparaffins.

Inventors: PEUTZ MARIUS GERARDUS FREDERIK, PEUTZ, MARIUS GERARDUS FREDERIKUS
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1994
Main classification: C10G69
IPC codes: C10G69, C10G61, C10G25, C10G7, C07C5, C10G35, C07C7